Some times there are thingies behind the knob that are stuck and don't move - if they are one direction the knob freezes up and won't move or if it is stuck the other direction the knob turns freely. So you need to remove the panel and look behind the knob for the thingies the knob was suppose to be turning and oil them with Tri-flow and free them up so things will move. It may also be that the knob is turning on the shaft and not hitting the thingie. In that case I'm just as stuck as you are - I have one like that. Mine may have a set screw that can help remove the knob, grind out a flat spot on the shaft and be returned after the thingy in the back works.